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B100r cardboard tube length?

Discussion in 'Amps [BG]' started by DrVenkman, Feb 13, 2014.

  1. DrVenkman

    DrVenkman

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    Just picked this amp up and as far as I can tell there are no cardboard tubes attached to the rear ports, or rolling around the bottom of the cab. I can figure out the diameter, but what's the length? Does the other end attach to anything? Any harm in leaving them off?
  2. AstroSonic

    AstroSonic Supporting Member

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    The port tubes have a 3 inch ID and a length of 5.7 inches. They are attached only at the back of the combo, via the plastic flares (rings). A little aquarium glue will securely attach them to the plastic rings and allow their removal should you want to try a different tuning. Otherwise they tend to come off. If you have not yet opened the speaker chamber (by removing the 15 inch driver), you may be surprised to find the tubes inside. That's where mine were when I received my B100R.
  3. DrVenkman

    DrVenkman

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    Thanks!

    Stupid question, how do I open it up as you suggest?
  4. AstroSonic

    AstroSonic Supporting Member

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    The grill cloth is stretched over a wood frame which is screwed onto the baffle board. Remove the four screws, but leave them in the grill board. Use the screws to pull the grill out.
  5. DrVenkman

    DrVenkman

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    Thanks again. I don't remember seeing screws on the front for the grill cloth but that just means I wasn't paying attention. I'll check it out tonight.
  6. AstroSonic

    AstroSonic Supporting Member

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    Mine is an American made from 96'. There could have been differences over the years. On mine the screws are close to the corners and not obvious.
  7. DrVenkman

    DrVenkman

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    From a little research online it sounds like some are held on with Velcro, so ill just have to check.
  8. giorob815

    giorob815 ... Supporting Member

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    Mine's American also, from the early '00s maybe (?), and uses velcro to attach the frame. Unfortunately, there's no 'tab' to pull, so one has to pry it off very carefully.

    Rob
    :bassist:
  9. giorob815

    giorob815 ... Supporting Member

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    And once again I post about 15 seconds too late, lol.

    Rob
    :bassist:
  10. P Town

    P Town Guest

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    My USA B100R also has Velcro, and no fabric loop to aid in removing the grill.
    I found that a LOT of force was required to remove it.

    I added a small strip of fabric loop to make it easier to remove the grill
  11. giorob815

    giorob815 ... Supporting Member

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    Ditto on adding a loop. Forgot to mention that.

    Rob
    :bassist:
  12. copacetic

    copacetic

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    I recall some years ago when discussing the cardboard tubes attached to the port holes on the B100R, that actually there was not much of a difference at all with or without them. The one suggestion for the best response in a room ( as opposed to an outdoor situation, where most likely the combo would be miked) was to place the amp 2-3 feet from a wall where those port holes would come into full effect with or without the tubes.
  13. AstroSonic

    AstroSonic Supporting Member

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    Interesting. I never ran mine without the tubes, but sim runs suggest a substantial difference that should be audible. Both have a peaked response, but with no tubes (Fb = 85Hz) there is a 7 db peak around 115 Hz; with the tubed (Fb = 50 Hz) there is a 3 db peak at about 105 Hz. Both plummet below the peak. By 60 Hz response is at -8 db w/o tubes and -4 db w. tubes. The driver is usefully loaded (helps prevent over excursion) to 54 Hz w/o tubes and to 37 Hz w. tubes. I wouldn't be surprised to find that some might prefer the tone w/o the tubes. It's a valid choice.
  14. DrVenkman

    DrVenkman

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    Just to beat this to death, does the material matter? If I used PVC instead of cardboard would it make any difference?
  15. AstroSonic

    AstroSonic Supporting Member

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    You could use PVC instead of cardboard in this application. Both are widely used for this (port tubes). With PVC you can file the sharp edge off the interior end to minimize turbulence (chuffing). At the spls this amp is capable of this may not be an issue. I used cardboard and have not had an issue with chuffing. Still, it won't hurt to smooth the edge a little (PVC or cardboard).
  16. DrVenkman

    DrVenkman

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    Thanks. Just thinking PVC might be easier to find.
  17. Lync

    Lync Supporting Member

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    I would remove the port trim (that is what I did with mine to put the cardboard ports back on when they fell off). My hand would not fit through the grommet trim, but when removed I could me get my hands inside the amp, get the ports, and then reattach them (no glue) to the grommet trim...they fit snug and I haven't had the issue since.
  18. DrVenkman

    DrVenkman

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    FYI I found that office supply stores sell mailing tubes that are 3" in diameter and work great for this.
  19. Bongolation

    Bongolation

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    I'm still trying to figure out how the original tubes got lost in the first place. Doesn't seem accidental, and a good deal more trouble than it conceivably could have been worth to do it intentionally.

    This thread got me on a quest to get my mint Yellville B-100R excavated from a pile of stuff in the corner of the bedroom and check if the tubes were there (yes).

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